We have found that follicle stimulating hormone (FSH) stimulates immature rat Sertoli cells in culture. The mechanism of action appears to involve the stimulation of both intracellular and extracellular cyclic adenosine monophosphate (cAMP). In adddition, this stimulation appears to require the integrity of specific, nonreceptor cell surface glycoproteins; also FSH modulates the types and quantities of Sertoli cell surface proteins. We therefore propose to 1) Investigate the role of surface proteins in the response of Sertoli cell to releases cAMP and to relate these surface proteins to changes in Sertoli cell metabolism in vitro and to the spermatogenic cycle in vivo. 2) Characterize and isolate FSH-induced Sertoli cell surface proteins and relate these proteins to Sertoli-Sertoli and Sertoli-germinal cell membrane interactions in vivo. 3) Investigate the hormonal modulation of fluid secretion by reformed testicular tubules in tissue culture and relate this modulation to specific ion fluxes and membrane permeases. 4) Investigate the roles of specific Sertoli cell proteins in the modulation of germinal cell development in vitro and in vivo. Techniques have been developed for the isolation, and the measurement of differentiation of purified populations of Sertoli cells and early germinal cells. The application of these purified cell populations and the isolation of purified preparations of cell-specific membrane proteins will, for the first time, allow us to dissect the specific membrane interactions between specific cell types and to test the roles of these interactions in the regulation of differentiation of male germinal cells.